The present invention relates to gradient index optical fibers and more particularly, to a method of assembling an array of fibers to form an imaging lens array which transmits an image of an object at an object plane to an image plane.
Image transmitters comprising bundled gradient index optical fibers are known in the art. U.S. Pat. No. 3,658,407 describes a light conducting fiber made of glass or synthetic resin which has a refractive index distribution in a cross section thereof that varies consecutively and parabolically outward from a center portion thereof. Each fiber acts as a focusing lens to transmit part of an image placed at, or near, one end. An assembly of fibers, in a staggered two-row array, transmit and focus a complete image of the object. The fiber lenses are produced under the trade name "SELFOC"; the mark is registered in Japan and owned by Nippon Sheet Glass Co., Ltd..
These gradient index lens arrays have found use in a number of technologies; e.g. in construction of printed type electrical circuits as disclosed in U.S. Pat. No. 3,922,062 and as a replacement for conventional optical systems in copiers as disclosed in U.S. Pat. Nos. 3,947,106 and 3,977,777.
The lens arrays used as optical systems in commercial copiers, e.g. Minolta EG301, Eskofot 1001, are typically assembled into a bundled two-row configuration by first manufacturing optical fibers having the required length and gradient index and then pressing the fibers together into an epoxy or resin mold. The fibers are separated by a distance in the order of 0.0319 mm when subjected to the maximum pressure permissable without injury to the fibers. The state of the art development of these arrays has heretofore been directed towards assembling these gradient index fibers in as close a proximity as possible. It has been discovered, however, as set forth in co-pending application U.S. Ser. No. 159,993 filed by William L. Lama on June 26, 1980 and assigned to the same assignee as the present invention, that the fiber spacing can be advantageously set at other values, some quite large relative to the present fiber spacing. More specifically, for a given gradient index lens fiber parameters (.sqroot.A, L, R) the exposure modulations onto an image plane can be minimized for a unique, but not obvious value of fiber spacing parameter b. The value of b is defined in the aforementioned application whose contents are herein incorporated by reference. For small inter-fiber spacings which do not greatly exceed the state-of-the-art spacing, a satisfactory spacing may be achieved simply by increasing the viscosity of the resin used in the assembly mold. However, for larger value of b, this expedient may not be sufficient.
It is, therefore, an object of the present invention to provide a method of assembling gradient index fibers into a lens array.
It is a further object to provide spacings between fibers which are larger then present known arrays.